The analysis seems to depend heavily on Nokia customers moving from Symbian phones to Windows devices, rather than to Androids, iPhones or BlackBerrys. The iPhone won't lose any significant market share -- it just won't gain any because Android is poised to rise even further and Microsoft's Nokia deal will fuel growth in WP7, IDC says.

"Up until the launch of Windows Phone 7 last year, Microsoft has steadily lost market share while other operating systems have brought forth new and appealing experiences," IDC analyst Ramon Llamas said in a press release. "The new alliance brings together Nokia's hardware capabilities and Windows Phone's differentiated platform. We expect the first devices to launch in 2012. By 2015, IDC expects Windows Phone to be [the] number 2 operating system worldwide behind Android."

How will this happen? IDC's analysis shows projected market share for 2011 and 2015. Nokia's Symbian mobile OS will drop from its 2011 share of 20.9% to only 0.2% by 2015, IDC said. Windows Phone 7 and Windows Mobile will rise from 5.5% in 2011 to 20.9% in 2015.

The iPhone, meanwhile, will drop from 15.7% to 15.3% over the next four years, and BlackBerry will decline from 14.9% to 13.7%. The Android boom will continue, moving from 39.5% market share in 2011 to 45.4% in 2015. iPhone and Android should both see significant revenue boosts because the smartphone market is growing so rapidly, with 450 million smartphones expected to ship in 2011 compared to 303 million in 2010.

IDC places a lot of faith in Nokia's power to tilt the market in Microsoft's favor, saying, "Nokia's recent announcement to shift from Symbian to Windows Phone will have significant implications for the smartphone market going forward."

But Microsoft may need help from more than just Nokia in order to turn things around, if the rise of Android is any indicator. Google's Android replicated the functionality of the iPhone, but instead of getting lost in the shuffle it soared past Apple by offering a wide variety of phones from various hardware manufacturers on all major carrier networks. But Android just had to beat the iPhone -- Windows Phone 7 will have to beat the iPhone while dozens of Android devices also call out to consumers.

Microsoft finds itself in the underdog role several years after CEO Steve Ballmer scoffed at the iPhone, saying, "There's no chance that the iPhone is going to get any significant market share." Last year, Ballmer was forced to admit, "We were ahead of this game and now we find ourselves No. 5 in the market ... We missed a whole cycle."

For what it's worth, IDC's numbers aren't the only ones available for measuring smartphone market share. Some even show greater progress for Windows than IDC is finding. The Nielsen Company says Windows already has 10% of the smartphone market, and also shows a different picture for Android, iPhone and BlackBerry. According to Nielsen, Android has 29% share followed by 27% each for Apple iOS and BlackBerry.

IDC predicts immediate growth for Android, saying that Android was in second place in 2010 (apparently behind Symbian) but will have twice as much market share as any competitor in 2011.